Differential-phase corrector



Nov. 1, 1960 Original Filed Deo. 17, 1956 '.J. H. CLARKDIFFERENTIAL-PHASE coRREcToR 2 Sheets-Sheet 1 2O (7 [/4 /3\ /2 /a s)PHAsE- RHASE- l) sH/FT/NG sH/ET/NO A a NETWORK NETWORK ,f 7

F/G 2 7 /2 6 9 w( 1 2 A 8 /23 s/lT//O /0 |11 2@ //6 25 NETWORK \26 24 22.1 \/6 |\l 20 Q/5 J4 2/ v .3 [7 f/ 5(29 rsa v( o O9 rsa A A I Q L L E@PHASE- 40 sH/ET/NG 56 NETWORK 37 /N VEN TOR J. H. CLARK ATTORNEY Nov. 1,1960 J. H. CLARK 2,958,832

DIFFERENTIAL-PHASE CORRECTOR Original Filed Deo. 17, 1956 2 Sheets-Sheet2 4a 49 f7 f 33 9 PHASE- TTENUTOR SHIFT/NG l- NETWORK- l- PHASE- A /9.-I X v 8 /O /63 65 PHASE- SHIFT/NG NETWORK k /N VEN TOR y J. H. CLARKATTORNEY United States DIFFERENTIAL-'PHASE CORRECTOR Jean H. Clark,Covina, Calif., assignor to American Telephone and Telegraph Company,New York, N.Y., a corporation of New York Continuation of applicationSer. No. 628,815, Dec. 17, 1956.` This application Oct. 20, 1959, Ser.No. 849,702

'5 Claims. (Cl. 333-28) This invention relates to wave transmissionnetworks and more particularly to a differential-phase corrector.

This application is a continuation of my application Serial No. 628,815,tiled December 17, 1956, now abandomed.

phase, causes a distortion of the color hue.

The object of the present invention is to correct Adifferential phase ofthe type just defined.

In accordance with the principle underlying the operation of thedilferential-phase correctors of the present invention, two componentsignals vare derived from the distorted input signal. These signals areunequal in magnitude and are either in phase or 180 degrees out of phasewith each other at low frequencies and have a relative phase shift of 90or 270 degrees at a selected higher operating frequency f. Theinequality in magnitude may be produced by amplifying one signal orattenuating the other, or by amplifying one and attenuating the other.The relative phase shift can be obtained in a phase-shifting network.One of these component signals is subjected to a dilerential treatmentand then the two signals are recombined. This dilierential treatment maybe provided by mixing the two signals through one or more controllable,nonlinear impedance devices. These devices are responsive to thesubstantially instantaneous current or voltage in the circuit. Thus, therelative phase shift of the output signal is `affected by the amount ofthe input signal which is allowed to pass through the nonlinear device,and the output signal becomes a function of the substantiallyinstantaneous voltage or current applied to the corrector. Means areprovided for adjusting 4the shape of current versus voltagecharacteristics of the nonlinear device, and also for providingdiiferent responses for different polarities of the applied voltage orcurrent.

-A plurality of nonlinear devices may be employed to yprovidesimultaneously available corrections for different polarities of thesignal and for dierent curve shapes. Also, biasing currents or voltagesmay be used to assist in obtaining the proper curve shapes to correctvarious distortions. Six embodiments Yof dilerential-phase correctors inaccordance with the present invention are disclosed herein, by way ofexample only. 'Three are for use with a balanced circuit and the otherswith unbalanced circuits. Each corrector comprises two transmissionpaths connected in parallel at their input ends and means associatedwith one of the paths for changing the amplitude of the signaltransmitted therethrough. These means may include an amplifier, anattenuator, or both. One of the paths includes also means for shiftingthe phase .pfthe signal approximately 90 degrees at the frequency f.

atent ICC One or more nonlinear impedance devices are connected in oneof the paths. When two are included in the same path, they may bearranged in parallel and oppositely poled so that each will respond toonly one polarity of the input signal. Means are also provided foradjusting the current-voltage characteristics of the nonlinear devices,means for adjusting the relative output voltages of the paths, and meansfor combining these voltages. When an amplifier is employed, aphase-shifting network mayjbe included, if required, to compensate forthe phase shift in the amplifier.

The nature of the invention and its various objects, features, andadvantages will `appear more fully in the following detailed descriptionof the typical embodiments illustrated in the accompanying drawing, ofwhich:

Fig. l is a schematic circuit of a balanced diierentialphase correctorin accordance with the invention, with `an amplifier and the -degreephase-shifting network both in the main signal path;

Fig. 2 shows schematically a modification of the corrector of Fig. l,with the 90-degree phase-shifting network in the control path;

Fig. 3 shows an unbalanced corrector employing two ampliliers in themain path;

Fig. 4 shows an unbalanced corrector using an attenuator;

Fig. 5 shows an unbalanced corrector with the '90- degree network in themain pathv and an amplifier in the control path; and

Fig. y6 shows an additional modification of Fig. l with thephase-shifting network at the input end of the control path and with thenonlinear devices differently arranged.

Taking up the iigures in greater detail, the balanced`differential-phase corrector of Fig. l comprises a main signaltransmission path 6 connected between a pair of input terminals 7, 8 anda pair of output terminals 9, 10. The path 6 includes an amplier 12 andtwo phaseshifting networks 13 and 14 connected in tandem. The amplifier12 has a phase shift of either zero or 180 degrees 'at the frequency f,which may be 4the color carrier frequency of a color television system.The network 13 is an all-pass structure having a phase shift of approveimately 90 degrees at f. The auxiliary network 14 compensates for anyphase distortion in the amplifier 12. The network 14 may be omitted insome cas, or its phase shift added to that of the network 13.

The branches 15 and 16 constitute `a second transmission path, connectedin parallel with the path 6 at their input ends. The branches 15 and 16are connected at their output ends to the adjustable tapping point 18 onIa voltage divider 19 shunted across the path 6 at its output end.

'Ihe parallel combination of two oppositely disposed, nonlinearimpedance devices 17 and 20 is connected in series with the branch 15.At their output ends, these devices are connected through a voltagedivider with an adjustable tapping point 21. The branch 16 includes twomore similarly arranged, nonlinear devices 23 and 24 connected at oneend through a voltage divider with an adjustable tapping point 25. Thedevices 17, 20, 23, and 24 may, for example, be crystal-diode,copper-oxide, selenium, or electron-tube rectiers, neon or similar-typegas tubes, or nonlinear resistors, capacitors, or ind-uctors. They areshown as rectiiiers. Each of these devices may be replaced by two ormore nonlinear devices, and biasing currents or voltages, or additionalseries or shunt resistors, may be employed as an aid in providing therequired characteristic to correct the distortion of the input signal.

If the points 18, 21, and 25 are centrally positioned, the correctorintroduces no correction. The branch 15 provides a positive phasecorrection. Moving the point 21 adjusts the correction between thepositive excursion of the input signal and the negative excursion. Thebranch 16 provides a negative phase correction, and the setting of thepoint 25 determines the distribution between the positive excursion andthe negative excursion. The setting of the point i3 and the choice ofthe gain furnished by the amplifier l2 determine the magnitude or therange of the correction. The gain of the amplier l2 may be madeadjustable and may be so set that there is no overall loss, or thatthere is even a gain, in the corrector. This is an important featurewhen a low-level signal is to be corrected.

If only a positive phase correction is required, the branch 16 may beomitted. If a negative correction only is required, the branch l5 may beomitted.

Fig. 2 shows a modification of the corrector of Fig. l. The 90-degreephase-shifting network 26 appears here in the phase-control path 28between the voltage divider 22 and the output end of the path 6. Thenetwork 13 is not required, and the auxiliary network 14 lhas also beenomitted. The circuit functions in the same way as the one shown in Fig.l, but has the advantage thereover that some transmission irregularityin the main path 6 is avoided by the removal of the networks 13 and 14.-In Fig. 2, the network 26 may be moved to the input end of the controlpath 28, if desired, without affecting the operation of the circuit.

Fig. 3 shows an unbalanced differential-phase corrector in accordancewith the invention employing two tandemconnected amplifiers 29 and 30 inthe main transmission path 31 and the network 33 in the control path 34.One side of the circuit may be grounded, as shown. Each of theamplifiers 29' and Si? has a phase shift of 180 degrees at f. Thenetwork 33 has a phase shift of approximately 90 degrees rat f. At theoutput end of the network 33, the path 34 divides into two branches, 35and 36. Positive phase correction is provided by the nonlinear impedancedevices 57 and 58 in the branch 35, which terminates at the adjustabletapping point 3S on a voltage divider shunted across the path 31 at apoint between the amplifiers 29 and 30. The branch 36, terminating atthe adjustable tapping point 39 on a voltage divider at the output endof the path 3l, takes care of negative phase correction by means of thenonlinear impedance devices 5'9 and 60. The setftings of the tappingpoints 40 and 4l on the resistors 32 and 37, respectively, determine thedistribution of the correction characteristics as between the positiveexcursion and the negative excursion. The settings of the points 38 and39 and the gains of the amplifiers 29 and 30 determine the magnitudes ofthe corrections. The phase network 33 may be shifted to the input end ofthe path 3l, if desired, but the position shown is preferred. Also, eachof the resistors 32 and 37 may be replaced by two adjustable resistors,arranged so that the resistance in series with each nonlinear device isindependently controllable, if desired. One of the branches 35 and 36may be omitted if only one type of phase correction is required.

Fig. 4 shows an unbalanced differential-phase corrector which requiresno internal amplifier, although one may be connected in tandemtherewith, if desired. The circuit comprises a phase-shifting network 42and an attenuator 47 connected in tandem in the signal path 43. One sideof the structure may be grounded, as shown. The control path 44 isconnected in parallel with the path 43, between the input terminal 7 andthe output terminal 9. The parallel combination of the two oppositelydisposed, nonlinear impedance devices 45 and 46 is connected in serieswith the path 44. These devices are shown as rectifiers. The output endof the rectifier 45 is connected to one end of a resistor having anadjustable tapping point 4S connected to the terminal 9. The rectifier46 is similarly connected to the terminal 9 through a resistor with anadjustable tapping point 49.

The attenuator 47 is preferably made adjustable, either continuously orin steps, so that the output voltage of the 7@ path 43 may be adjustedto provide the required curve shape to compensate the distortion. Thenetwork 42 has a phase shift of approximately 90 degrees at f. Thus, a.voltage which may be adjusted in amplitude by the attenuator 47 andshifted in phase by the network 42 is cornbined at the output terminals9 and 16 with a voltage from the path 44. This circuit provides onlypositive phase correction. The setting of the tapping point 49determines the magnitude of the `correction on the positive excursionand the position of the point 48 controls the correction on the negativeexcursion.

The unbalanced circuit of Fig. 5 is similar to the one shown in Fig. 4except that the amplitude-adjusting means comprise an amplifier 56 inthe control path S1 instead of an attenuator in the signal path 53. Theamplifier 50 is terminated in a voltage divider 54 with an adjustabletapping point 55 to which the input ends of the rectifiers 45 and 46 areconnected. The setting of the point 55 determines the shape of thecorrection characteristic. The correction is a positive phase shift ifthe amplifier 50 has zero phase shift at f. The correction is negativeif the phase shift of fthe amplifier 50 is 18() degrees at f. Thesettings of the points 48 and 49 control the correction on the negativeexcursion and the positive excursion, respectively. The gain of theamplifier 5i) may be so selected or adjusted that there is no overallloss in the corrector. The phase network 40 may be removed from the path53 and inserted in the control path 51, either before or after amplifier50, without altering the operation of the circuit.

Fig. 6 shows another balanced differential-phase corrector which is amodified form of the one shown in Fig. l. The main signal path 62includes only the amplifier l2 and the voltage divider 19 with tappingpoint 18. The network 63, located at the input end of the phase-controlpath 64, has a phase shift of approximately 90 degrees, plus or minusany phase compensation required for the amplifier l2, at the frequencyf. At the output end of the network 63, one side 65 of the path 64divides into two branches, 66 and 67, and the other side 63 divides intothe branches 69 and 70. The nonlinear impedance devices 72, 73, 74, and75, show-'n as reetifiers, are connected, respectively, in the branches66, 67, 69, and 70. The branches 66 and 69 are connectd at their outputends through a voltage divider 77 having an adjustable tapping point 78.The branches 67 and 70 are likewise connected through another voltagedivider 79 having an adjustable tapping point 80. The points 78 and 86are connected to the point 18.

The rectifiers 72 and 74 control the correction on the positiveexcursions of the signal and the rectifiers 73 and 75 control on thenegative excursion. The settings of the points 73 and Si) determinewhether the correction is a positive or a negative phase shift. The gainof the amplifier l2 and the setting of the point 18 determine themagnitude of the correction.

It is to be understood that the above-described arrangements are onlyillustrative of the application of the principles of the invention.Numerous other arrangements may be devised by those skilled iu the artwlthout departing from the spirit and scope of -the invention. Forexample, when the nature `of the distortlon 1s such that one or more ofthe nonlinear impedance dev ices are seldom or never needed in order toprovide satlsfactory equalization, they may be omitted, since theirinclusion would serve no useful purpose for that particular application.Also, it is evident that any of the equallzers-dlsclosed may include anamplifier in one of the parallel transmission paths and an attenuator inthe other.

What is claimed is:

l. ln a color television system in which changes 1n the amplitude of theluminance signal cause changes in the relative phase of the colorcarrier signal with respect to a .reference synchronizing signal, anetwork for cornpensating these phase changes comprising a pan' of 111-put terminals, a pair of output terminals, a phase-Shifting network andan attenuator connected in tandem between the input terminals and theoutput terminals, two rectiers with unlike electrodes connected to aninput terminal, a path including a resistor connected between theremaining electrodes of the rectiliers, and a connection from theresistor to an output terminal.

2. In a color television system in which changes in the amplitude of theluminance signal cause changes in the relative phase of the colorcarrier signal with respect to a reference synchronizing signal, anetwork for compensating these phase changes comprising a pair of inputterminals, a pair of output terminals, a phase-shifting network and anattenuator connected in tandem between the input terminals and theoutput terminals, and the series combination of a rectifier :and aresistor connected between an input terminal and an output terminal.

3. In a color television system in which changes in the amplitude of theluminance signal cause changes in the relative phase of the colorvcarrier signal with respect to a reference synchronizing signal, anetwork for cornpensating these phase changes Icomprising a pair ofinput terminals, a pair of output terminals, a phase-shifting network`and amplitude-changing means connected in tandem between the inputterminals and the output terminals, two rectiiers with unlike electrodesconnected to an input terminal, a path including a resistor connectedbetween the remaining electrodes of the rectiers, `and a connection fromthe resistor to an output terminal.

4. In a color television system in which changes in the amplitude of theluminance signal cause changes in the relative phase of the colorcarrier signal with respect to a reference synchronizing signal, anetwork for compensating these phase changes comprising a pair of inputterminals, a pair of output terminals, two transmission paths betweenthe input terminals and the output terminals, a phase-shifting networkin one of the paths, amplitude-changing means associated with one of thepaths, and one of the paths including two rectiers with unlikeelectrodes connected to an input terminal, a path including a resistorconnected between the remaining electrodes of the rectiers, and aconnection trom the resistor to an output terminal.

5. In a color television system in which changes in the amplitude of theluminance signal cause changes in the relative phase of the colorcarrier signal with respect to a reference synchronizing signal, anetwork for compensating these phase changes comprising a pair of inputterminals, a pair of output terminals, two transmission paths betweenthe input terminals and the `output terminals, a phase-shifting networkin one of the paths, amplitude-changing means associated with one of thepaths, and the series combination of a rectifier and a resistorconnected in series in one of the paths.

References Cited in the ile of this patent UNITED STATES PATENTS2,252,002 Halsey Aug. 12, 1941 2,444,063 Pfleger June 29, 1948 2,776,410Guanella Ian. 1, 1957 2,849,546 Martin Aug. 26, 1958

